(a) Technical Field
The present invention relates to a complementary metal oxide semiconductor (CMOS) image sensor and a method for fabricating the same, and, more particularly, to a complementary metal oxide semiconductor (CMOS) image sensor capable of effectively preventing a cross talk effect and a method for fabricating the same.
(b) Description of the Related Art
In general, semiconductor image sensors are semiconductor devices for converting an optical image into electrical signals and may be a charge coupled device (CCD) image sensor or a CMOS image sensor. Research efforts have been made to increase photosensitivity of the image sensors and a light concentration technique has been introduced.
For example, a CMOS image sensor comprises a photo-detecting element for sensing light and a logic circuit for converting sensed light into electrical signals. The photo-detecting element typically includes a photodiode. For fabrication of a CMOS image sensor, a ratio of the area of the photo-detecting element to the entire area of the CMOS image sensor (referred to as “full factor” typically) has to be increased in order to increase the photosensitivity.
However, the full factor is limited to the extent that the logic circuit also has to be formed within the area of the CMOS image sensor.
Many light concentration techniques have been studied which change the path of light incident on regions of the CMOS image sensor other than on the photo-detecting element. One example of such light concentration techniques is a technique of forming a micro lens on an upper portion of a color filter of the CMOS image sensor, which may be described with reference to FIG. 1.
In FIG. 1, a conventional CMOS image sensor includes a semiconductor substrate 100, device isolation regions 102 on the semiconductor substrate 100 for isolating one device from another device, CMOS devices 106 including photodiodes 104 in device regions between device isolation regions 102, a wire-insulating layer 108 on both device isolation regions 102 and CMOS devices 106, and a first metal wire M1 on wire-insulating layer 108, wherein the first metal wire M1 passes through wire-insulating layer 108 and provides contact to CMOS devices 106.
In addition, the CMOS image sensor further includes a first inter-wire-insulating layer 110, a second metal wire M2, a second inter-wire-insulating layer 112, a third metal wire M3, and a third inter-wire-insulating layer 114, which are sequentially layered on the wire-insulating layer 108 as shown in FIG. 1.
Also, the CMOS image sensor further includes color filters R, G, and B, a planarizing layer 116, and micro lenses 118, which are sequentially layered on the third inter-wire-insulating layer 114.
With such a structure of the CMOS image sensor, external light A, B, C, and D are concentrated on the photodiodes 104 of the CMOS devices 106 after passing through the micro lenses 118. However, part of the light, such as light beams A and D, incident on edges of micro lenses 118 are significantly refracted and may be incident not on a CMOS device of a corresponding pixel, but on CMOS devices of adjacent pixels.
Such a phenomenon that light passing through the micro lenses 118 is incident on the CMOS devices of adjacent pixels, referred to as “cross talk,” produces unnecessary noise components, thereby deteriorating characteristics of the CMOS image sensor.
U.S. Pat. Nos. 6,057,538 and 6,639,293 disclose image sensors which reduces the cross talk. However, the image sensors disclosed in these patents have restrictions on effective avoidance of the cross talk.